The present invention relates generally to vehicle brake assemblies, and in particular, to a high friction brake assembly incorporating a plurality of backing plate extensions through a friction material matrix, to be utilized in vehicle parking brakes and vehicle emergency braking systems on vehicle equipped with a separate typical, full service brake system (disc or drum) at each of its four wheels.
Vehicle drum type friction brakes commonly include a vehicle brake shoe assembly carrying a frictional matrix which is brought into contact with an inner cylindrical surface of a rotating brake drum to generate a frictional force and correspondingly slow, stop, or hold the vehicle in a stationary or parked position. Disc brake systems include a caliper assembly having opposing friction pads which are brought into contact with a rotor disc.
Variations between the friction surface of the brake assembly and the surface of the rotating brake member (drum or disc) can alter the frictional effectiveness of a friction brake during its initial instances of use. For example, if the friction level generated by a friction brake is too low due to regions of the frictional matrix which are not in contact with the opposing friction surface of the brake drum or rotor, the brake will not function to the required level of static effectiveness, i.e. parking brake capability. One method commonly utilized to overcome this type of static friction problem is to bring the vehicle to a stop a number of times using only the parking brake or emergency brake, thereby generating excessive frictional forces on those portions of the brake assembly in contact with the rotating brake drum or rotor, and wearing or abrading them into closer conformance with the surface of the rotating brake drum or rotor. Such methods are prone to neglect by the average operator. If performed in an improper manner, these methods can lead to premature failure or excessive wear on the brake components.
Alternatively, frictional braking forces can be increased in vehicle friction brakes by producing a rough or sandblasted friction surface on the brake drum or rotor which is engaged by the brake shoe or pad assembly. This process, while increasing the frictional braking forces in the initial periods, may accelerate attrition of the friction material, shortening the lifespan of the brake components such as the brake friction material matrix.
The use of backing plate extensions, nubs or teeth, which are completely contained within, and engage with, the brake friction material matrix on brake shoe and pad assemblies, has been previously employed to facilitate the attachment and interlocking of the brake friction material matrix to the backing plate. See, for example, U.S. Pat. No. 6,367,600 B1 to Arbesman and U.S. Pat. No. 6,279,222 B1.
Another example of the use of projecting nubs or teeth is seen in U.S. Pat. No. 4,569,424 to Taylor, Jr., where a brake shoe assembly is provided. A friction material matrix in the '424 Taylor, Jr. reference is molded directly onto a brake liner plate which includes a plurality of perforations forming protruding tabs. The inter-engagement between the molded friction material and the perforated areas and tabs provides an enhanced interlocking strength between these elements. The '424 Taylor, Jr. reference, specifically teaches that it is undesirable for the protruding tabs to extend so far as to reach the outer surface of the friction material matrix, and indicate that the brake shoe assembly has reached the end of a useful service life when sufficient friction matrix material has been worn away so as to expose the protruding tabs.
Accordingly, there is a need in the automotive brake systems design area for a parking brake or emergency brake assembly with enhanced static and dynamic frictional properties, and which does not require an initial wear or break-in period to improve conformance between the frictional matrix and the opposing frictional surface of the brake drum or rotor.